This invention relates to a cannula used for endoscopic surgery, and more particularly to a cannula and method for maintaining a clear visual field for an endoscope housed within the cannula.
Endoscopic surgery allows a surgeon to perform safe and successful procedures because of the surgeon""s ability to view the surgical site through the endoscope lens. For some surgical procedures, such as dissection, the cannula housing the endoscope has a transparent blunt dissection tip through which the surgeon views the surgical site. The blunt dissection tip protects the endoscope lens from being smeared by blood or fatty tissue present at the surgical site, or from being fogged due to the moist subcutaneous environment, However, many surgical procedures cannot be performed using a blunt dissection tip, When side branches and vessel ends of a vessel must be transected to harvest the vessel, the end of the cannula must be open to allow the surgical tools to extend from the cannula, When the cannula end is open, the endoscope lens is subject to the adverse conditions described above, The surgeon is forced to repeatedly remove the cannula from the body to clean the endoscope lens, This increases the length and risks of the operation,
Some conventional schemes for cleaning an endoscope lens rely upon an endoscope with a cleaning system built within it. However, having a cleaning system within the endoscope restricts the angle of incidence at which the cleaning fluid may be propelled toward the lens to almost parallel to the lens. This results in a less effective cleansing action. Also, since the spray is being directed parallel to the lens, the surgeon cannot see the spray source and it is therefore difficult to adjust the direction of the spray. Thus, with these systems, the endoscope must still be removed on occasion for manual cleaning where the proper angle of incident spray can be obtained manually. Additionally, in procedures using gas insufflation, the gas may dry out a target vessel or other surgical site. In these situations, it is often necessary to irrigate the vessel to prevent the vessel from drying out. However, conventional endoscope washing systems are not capable of providing both endoscope lens cleaning and remote surgical site irrigation. Therefore, a remote endoscopic washing system would be desirable for more effectively cleansing the endoscope lens during a surgical procedure by allowing the surgeon to control the angle at which cleansing fluid is sprayed as well as allowing the surgeon to use the same apparatus to irrigate the surgical site itself.
In accordance with the present invention, a retractor is positioned within a cannula with a dissection cradle end of the retractor positioned at the distal end of the cannula. The retractor includes a first portion that has an axis approximately parallel to a central axis of the cannula, and a second portion that has an axis which is at an angle with respect to the central axis of the cannula. The dissection cradle is located at the distal end of the second portion of the retractor. In another embodiment, the retractor includes two legs having substantially parallel axes that selectively protrude from the distal end of the cannula. The protruding legs support the dissection cradle formed in the shape of a partial loop that is positioned in a plane skewed relative to the axes of the legs, with a bottom of the loop directed away from the cannula. Thus, in operation, when the surgeon locates a vein and side branch of interest, the surgeon extends the retractor to cradle the vein in the dissection cradle. Once cradled, the retractor may be fully extended. displacing the vein away from the axis of the cannula, causing the side branch to be isolated and exposed to a surgical tool. The surgical tool may then be extended from within the cannula to operate on the isolated and exposed side branch.
In accordance with one embodiment of the present invention, a remote irrigation system is built into the cannula. In one embodiment, one of the legs which comprise the retractor of the present invention is hollow, and is attached to a spray nozzle disposed in the distal end of the retractor. The proximal end of the hollow leg is attached to a fluid input tube which selectively provides irrigation fluid under pressure for washing the endoscope lens. When extended slightly beyond the distal end of the cannula, the spray nozzle is positioned to direct the spray of irrigation fluid at an angle approximately normal to the endoscope lens. This provides for an extremely effective cleaning action, and minimizes the need for removal of the endoscope during surgical procedures for manual cleaning. Additionally, if the surgical site itself requires irrigation, the retractor is extended out of the cannula toward the area requiring irrigation, and an irrigation fluid can be sprayed directly on the site. Finally, as the spray is directed back toward the lens, the surgeon can visually adjust the extension of the retractor to accurately direct the spray toward the lens or surgical site.
In a further embodiment, the hollow leg moves within a lumen in the cannula in fluid-resistant sliding engagement, and the fluid inputs tube is coupled to this lumen. In this embodiment, the maximal outer dimension of a region of the hollow leg is slightly less than a maximal inner dimension of the lumen. The slip-fit, fluid-resistant coupling of the hollow leg within the lumen allows irrigation fluid to be introduced at the proximal end of the lumen by the fluid input tube without significant leakage past the sliding juncture of the hollow leg within the lumen.
In an alternate embodiment, the hollow leg includes a semi-rigid plastic tubing, and fits within an irrigation tube which lines the inside of the lumen. The fluid input tube attaches to the irrigation tube and extends out of the cannula handle for receiving irrigation fluid. The use of flexible, semi-rigid plastic tubes provides fluid seals throughout the irrigation system to minimize leakage. In a third embodiment, the cannula contains a separate irrigation lumen which has a spray nozzle disposed in a fixed position at its distal end. The spray nozzle is positioned within the cannula to allow the proper angle of incidence for the spray to effectively clean the lens. Finally, in another embodiment, the dissection cradle is supported by only one leg, and the lumen which previously held the second leg instead is fitted with a spray nozzle directed toward the endoscope lens. An embodiment is also disclosed :in which a nozzle tube situated within a cannula lumen is selectively extensible responsive to the application of hydraulic pressure.